THAT'S HOT: Energy company Dalkia shows how the firm's system turns excess heat from a data center's cooling units into heating for a business park. (Photo: Dalkia)

Anyone who has worked with a desktop computer knows how it can warm up the room. Now, at one business park in France, the heat coming off computer servers actually contributes to warming the buildings through a district heating network.

Data centers house computing equipment for online services and other companies. They require plenty of electricity, both to run the equipment inside and to cool them, making them responsible for 2 percent of the world's carbon dioxide emissions, according to think tank Sustainia. Many researchers are working on ways to make them more environmentally friendly.

The Val d'Europe, a business park serving Disneyland Paris, reuses the heat from a nearby data center's air-conditioning units. Heat exchangers capture the excess energy and use it to heat water to 131 degrees Fahrenheit (55 degrees Celsius). The data center pipes the hot water to a central plant, which distributes it to the business park.

Once the hot water reaches a building, it enters the building's substation, where it transfers its heat to the building's hot-water system. The now-cool water returns to the central pipe.

The system, created by the French energy company Dalkia, heats about 6 million square feet (600,000 square meters, or about a fifth of a square mile) of office space, according to Dalkia. It creates no emissions.

Dalkia's system is one of the world's first to pipe excess energy from a data center to a network serving several buildings some distance away. Other data centers have tried to reduce their carbon footprints by using the energy to heat one building nearby or to heat a swimming pool or greenhouse. In 2009, a data center below the Uspenski Cathedral in Helsinki, Finland, garnered attention for plans to use its excess energy to heat 500 area homes.

Dalkia earned a listing in Sustainia 100, a catalog of 100 promising sustainability solutions that the think tank published June 20 at the United Nations' Rio+20 conference. The conference has attracted some criticism for weak results, but Sustainia 100 aimed to show positive activities are already under way.